An autoimmune disease is a condition in which the body's immune system mistakenly identifies its own healthy cells, tissues, and organs as foreign invaders.
Instead of protecting the body from external threats like bacteria or viruses, the immune system produces antibodies that attack its own host. This internal misfire can cause chronic inflammation, tissue damage, and a wide range of debilitating symptoms, manifesting in well-known conditions such as rheumatoid arthritis, lupus, type 1 diabetes, and multiple sclerosis.
In short, it is a case of biological friendly fire, where the body's natural defence system becomes its own worst enemy.